Granular matter filled weapon guidance electronics unit

ABSTRACT

A guidance electronics unit is provided for an explosively-launched vehicle, e.g., a projectile or missile, comprising a plurality of circuit card assemblies, each circuit card assembly containing a plurality of electronic components and interconnections, each circuit card assembly maintained in a housing and spaced apart. All spaces surrounding each circuit card assembly are filled with a granular material to provide support for each circuit card assembly during explosive launch. Further, a method for supporting circuit card assemblies in the guidance electronics unit is provided. The problem of enabling guidance electronics to survive the large loads encountered during an explosive launch out of a gun, such as a howitzer, or missile launch tube is thereby solved.

TECHNICAL FIELD

The present invention is directed to guidance electronics units, and,more particularly, to stabilizing circuit cards in such units so as toavoid damage during the shock of gun launch.

BACKGROUND ART

Guided weapon design necessitates the need for a guidance electronicsunit (GEU), which is the brain of the system. The GEU includes functionssuch as the mission computer, guidance, navigation, and control of theweapon, along with other weapon specific functions. The GEU consists ofmultiple circuit card assemblies (CCAs) that are usually arranged inclose proximity to each other.

Guidance electronics units (GEUs) are used in a variety of weapons thatare subject to sudden forces during an explosive launch, such as firingthe weapon from a gun or howitzer or launching a missile.

Typical designs for a guidance electronics unit consists of circuit cardassemblies held together by metal housings, often with very precisemachining. These metal housings are very expensive to produce and take along time to design and develop.

U.S. Pat. No. 4,888,663, entitled “Cooling System for ElectronicAssembly”, and issued on Dec. 19, 1989, to Ernest P. Longerich et al,and related U.S. Pat. Nos. 4,922,381 and 4,903,603, disclose a pluralityof circular circuit cards, arranged in an aligned, parallel relationshipin a sealed unit. An electrically insulating coolant liquid is disposedin the sealed unit in direct contact with the circuit cards andelectrical components mounted thereon to absorb heat generated byelectrical power dissipation. For extremely high “G” forces, in excessof 100,000 G, a plurality of ceramic circuit cards is spaced apart by aplurality of ceramic spacer cards and bolted together.

However, it appears that there is little prior art that deals withprotecting rigidly-mounted guidance electronics units against the shockof explosive launch. For example, U.S. Pat. No. 4,949,917, entitled“Gyro Stabilized Optics with Fixed Detector”, issued on Aug. 21, 1990,to Wilber W. Cottle et al, illustrates a plurality of circuit cardassemblies (CCAs), but no mechanism is disclosed or suggested forprotecting the CCAs during an explosive launch, such as from a howitzer.

Thus, there remains a need for supporting the internal components of aguidance system, and, in particular, for stabilizing circuit cardassemblies and their interconnects in such guidance electronics units soas to avoid damage during the shock of an explosive launch.

DISCLOSURE OF INVENTION

In accordance with the present invention, granular material is used toessentially completely fill the void in the guidance housing andsurround the circuit card assemblies so that there is little chance thatanything can move. Such granular material, which is similar to theconsistency of fine beach sand, does not compress during the shock ofgun launch; consequently, no damage to any of the circuit cards orcomponents on the cards occurs. The granular material surrounds thecircuit cards so that any loads on the guidance electronics unit aredistributed much more equally throughout the circuit cards. The granularmaterial also holds large components in place so that they survive anyshock or vibration loads that are often made worse due to their mass.

More specifically, in accordance with the present invention, a guidanceelectronics unit is provided for an explosively-launched vehiclecomprising a plurality of circuit card assemblies, each circuit cardassembly containing a plurality of electronic components andinterconnections, each circuit card assembly maintained in a housing andspaced apart. All spaces surrounding each circuit card assembly arefilled with the granular material to provide support for each circuitcard assembly during explosive launch.

Further in accordance with the present invention, a method is providedfor supporting the circuit card assemblies in the guidance electronicsunit. The method comprises:

-   -   placing each circuit card assembly in the housing in a stacked,        spaced apart configuration, and    -   substantially filling all spaces surrounding each circuit card        assembly with a granular material to provide support for each        circuit card assembly during explosive launch.

The present invention solves the problem of making it possible forguidance electronics to survive the large loads encountered during anexplosive launch out of a gun or howitzer. The teachings of the presentinvention may also be used in a guided missile electronics unit using ahollow glass sphere fill material, so that the weight of the fillmaterial is not an issue.

No known Weapons Guidance Electronics Unit uses granular matter as thestructural support of the circuit cards. The present invention coulddramatically decrease cost, while increasing simplicity, reworkability,and survivability of numerous weapons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a prior art cannon-launched guidedprojectile;

FIGS. 2 a-2 b are enlarged views of the guidance section of theprojectile of FIG. 1, with FIG. 2 a showing an exploded view and FIG. 2b showing an assembled view, without attachment of the radome;

FIGS. 3 a-3 b depict a common prior art approach to supporting circuitcard assemblies in guidance electronics units, with FIG. 3 aillustrating the structure before explosive launch and FIG. 3 billustrating the structure resulting in “oil-canning” during explosivelaunch; and

FIGS. 4 a-4 b depict the analogous structures resulting from theteachings of the present invention, with FIG. 4 a illustrating thestructure before launch and FIG. 4 b illustrating the structure duringlaunch.

BEST MODES FOR CARRYING OUT THE INVENTION

Nearly all weapons undergo significant mechanical shock and vibrationloads due to harsh environments to which they are exposed. Theseenvironments can include such things as transportation, launch, andcaptive carry on an aircraft. These loads cause the guidance electronicunit (GEU) to use a structural cage, usually made out of metal, toconstrain the GEU circuit card assemblies (CCAs) to ensure that thesensitive electronic components on the GEU CCAs and the electricalinterconnections remain functional.

FIG. 1 depicts a common projectile 10, such as a cannon-launched guidedprojectile. The projectile 10 comprises a base section 12 at its aftend, and proceeding from the aft end to the forward end a propulsionsection 14, a payload section 16, and a guidance section 18.

The base section 12 includes a plurality of stabilizing fins 20, whichin the firing position are held flush with the outer surface of the basesection 12 by latching mechanism 22. When the projectile is fired, aslipping obturation band 24 seals the projectile against the interior ofthe cannon barrel (not shown) to prevent the escape of propulsion gases.When the spinning projectile leaves the cannon barrel, the stabilizingfins 20 are deployed to stabilize the projectile in flight.

The propulsion system 14 includes a rocket motor (not shown) and ignitor(not shown), as is well-known for such projectiles.

The payload section 16 includes a warhead (not shown) and ignitor (notshown), as is well-known for such projectiles.

The payload section 16 includes a warhead (not shown) and fuze (notshown), as is well-known for such projectiles. The warhead may be, forexample, a typical high explosive 155 mm howitzer shell, or otherexplosive material, such as used in sudden launch munitions, including,but not limited to, projectiles, missiles, and the like.

The guidance section 18 comprises a control section 26 and a guidancenavigation unit 28 (shown in greater detail in FIGS. 2 a-2 b). Thecontrol section 26 includes a plurality of canards 30 which are actuatedby servo actuators 32, as well as one or more thermal batteries (notshown). The servo actuators 32 are actuated by the output signals of theguidance navigation unit.

The guidance navigation unit (GNU) 28 is shown more completely in FIGS.2 a-2 b, which depict the details of the guidance section 18, andincludes, in order from aft to forward end, a GNU base plate 34, aguidance electronics unit (GEU) 36 that comprises a plurality of circuitcard assemblies (CCAs) 38, an inertial measurement unit (IMU) mountingplate 40 on which the IMU 42 is mounted, and a super capacitor assembly44 that acts as a power supply. The GNU 28 is housed in a housing 46. Aglobal positioning satellite (GPS) antenna 48, comprising two circuitcards, is mounted on the outside of the housing 46. A radome 50 coversthe entire GNU 28, and is transparent to the radio frequency (rf)radiation received by the GPS antenna 48. There are additional sensors,electronics, and interconnects in the GNU that are not shown here, andare not relevant to the teachings herein. Such additional components,however, are well-known to those skilled in this art.

The GEU 36 comprising the plurality of circuit card assemblies 38described above is shown in greater detail in FIGS. 3 a-3 b and 4 a-4 b.

FIGS. 3 a-3 b depict a common prior art approach to supporting circuitcard assemblies in guidance electronics units, with FIG. 3 aillustrating the structure before explosive launch and FIG. 3 billustrating the structure during explosive launch, resulting in “oilcanning”, or bending of each circuit card assembly 38. Each circuit cardassembly 38 supports a variety of electronic components 52 and iscontained in housing 54. Specifically, each circuit card assembly 38 issupported on a structure 56 that sup ports the circuit card assemblyaround its perimeter.

During explosive launch, such as from a gun, the G forces are sufficientto cause “oil caring”, as the circuit card assemblies 38 bend inreaction to the gun shock force. Such bending adversely impacts theelectronic components 52 and their interconnections, due to thesensitivity of the multiple bonds between the electronic components andthe circuit card assemblies. The amount of displacement in FIG. 3 b isexaggerated to show the effect on the bonds between electronicscomponents 52 and circuit card assemblies 38.

In accordance with the present invention, the space between each circuitcard assembly 38 is filled with a granular matter 58, thereby obviatingthe need for supporting structure 56, as shown in FIG. 4 a. Duringexplosive launch, the granular matter 58 uniformly supports each circuitcard assembly 38, and there is no bending of the circuit card assembliesas a result of the shock force. The circuit card assemblies 38 remain inplanar configuration, and the electronic components 52 are not adverselyimpacted by the explosive launch.

The circuit card assemblies 38 are held in spaced-apart configuration bya holder 60 (shown also in FIGS. 2 a-2 b), which does not support thecircuit cards during explosive launch but rather spaces the circuitcards apart during filling with the granular matter 58. Accordingly, theholder 60, also shown in FIGS. 4 a-4 b, is made of a lightweightmaterial, such as fused powder nylon or injection-molded plastic.

The granular matter 58 fills up the spaces between the circuit cardassemblies 38 to the point necessary to support them, the electroniccomponents 52 thereon, and the electrical interconnects thereto.

The present invention eliminates the need for a rigid cage, orstructure, 54 by using the granular matter 58 essentially as a pottingcompound that can be filled and removed if necessary. Utilizing mediafor a potting compound that can be removed in lieu of more permanentpotting compounds such as epoxies allows for disassembly and rework ofthe system. Being able to remove the granular matter 58 allowsdisassembly and rework of the GEU, which is almost always a necessity inguided weapons development, has advantages during production, such aspost-lot acceptance testing analysis.

The granular matter 58 chosen for this application was glass beads,which are small pieces of glass having a diameter smaller than 250microns (10 mils; 0.010 inch). Hollow glass spheres, referred to as“microballoons” are a viable alternative in order to reduce the weightof the GEU 36, since the density of microballoons is approximately{fraction (1/9)}th that of glass beads. There are a myriad of viablegranular matter alternatives that would serve the same function as glassbeads and allow the granular matter 58 to be removed from the system.Some of these alternatives provide thermal transfer by having higherthermal conductivity than glass beads, which are a very good insulator.This is important in cases where the electrical components heat upduring use and the heat needs to be dissipated. Other alternativesprovide electromagnetic interference advantages, by shielding the systemor components from electromagnetic waves that are harmful to the systemor components, or by preventing the system or components fromtransmitting specific electromagnetic frequencies that are harmful toother systems or components.

While a number of various granular matter 58 may be used in the practiceof the present invention, glass beads are preferred. Microballoons,though of lower density, are less structurally tolerant of high G forcesthan are glass beads.

Glass beads are presently commercially available in three size ranges:“coarse” (0.0059 to 0.098 inch), “fine” (0.0035 to 0.0059 inch), and“extra fine” (0.0017 to 0.0035 inch). A blend of various size ranges maybe used, for better close-packing. However, glass beads of a single sizerange (e.g., “coarse”) may alternatively be used, with no measurabledifference in performance between single size ranges and blended sizeranges.

The granular matter 58 provides unilateral support of the CCAs 38 insidethe GEU 36. During static and dynamic environments, each CCA 38 issupported along the entire surface of each of the boards. There islittle to no point loading of the CCAs 38 from the assembly fixture orcardholder 60, thereby preventing phenomena such as “oil-canning” (shownin FIG. 3 b) from causing failures in the electronic components 52. Thestress pattern observed in a granular matter under compression is shownin FIG. 34, page 60 of the book Sands, Powders, and Grains: AnIntroduction to the Physics of Granular Materials, by Jacques Duran. Thetext of the book describes the phenomenon of the granular matter, that“the (vertical load) stress tends to be redirected laterally toward thevertical walls”.

A tightly packed granular matter GEU would, therefore, redirect loadslaterally to the direction of the load, allowing the load to be spreadover the entire filled cavity and allow the GEU to withstand loads fromany direction. Tightly packing the granules 58 into the GEU isaccomplished by vibrating the housing 46 during the fill process. Thisallows the granules 58 to pack well and also reduces the time it takesto fill the GEU.

While the foregoing description has been primarily directed toexplosively-launched projectiles, such as from guns, it will be readilyappreciated by those skilled in this art that the same teachings may beadvantageously employed in missiles, which are also explosively launchedfrom missile tubes. Such missiles also include a unit equivalent to theprojectile's guidance electronics unit, called a “guide missileelectronics unit”, comprising a plurality of circuit card assemblies,which are also subject to high G forces upon launching.

INDUSTRIAL APPLICABILITY

The use of granular material to support circuit card assemblies inguidance electronics units and guided missile electronics units isexpected to find use in explosively-launched vehicles.

1. A guidance electronics unit for an explosively-launched vehiclecomprising a plurality of circuit card assemblies, each circuit cardassembly containing a plurality of electronic components andinterconnections, each circuit card assembly maintained in a housing andspaced apart, wherein all spaces surrounding each circuit card assemblyare filled with a granular material to provide support for each circuitcard assembly during explosive launch.
 2. The guidance electronics unitof claim 1 wherein said granular material has a particle size less than250 microns.
 3. The guidance electronics unit of claim 2 wherein saidgranular material comprises at least one particle size range.
 4. Theguidance electronics unit of claim 3 wherein said granular materialcomprises more than one particle size range.
 5. The guidance electronicsunit of claim 2 wherein said granular material comprises glass beads. 6.The guidance electronics unit of claim 2 wherein said granular materialcomprises microballoons.
 7. The guidance electronics unit of claim 1wherein said explosively-launched vehicle is selected from the groupconsisting of guided projectiles and missiles.
 8. A method forsupporting circuit card assemblies in a guidance electronics unit for anexplosively-launched vehicle, each circuit card assembly containing aplurality of electronic components and interconnections, said methodcomprising: placing each circuit card assembly in a housing in a spacedapart configuration, and substantially filling all spaces surroundingeach circuit card assembly with a granular material to provide supportfor each circuit card assembly during explosive launch.
 9. The method ofclaim 8 wherein said granular material has a particle size less than 250microns.
 10. The method of claim 9 wherein said granular materialcomprises at least one particle size range.
 11. The method of claim 10wherein said granular material comprises more than one particle sizerange.
 12. The method of claim 9 wherein said granular materialcomprises glass beads.
 13. The method of claim 9 wherein said granularmaterial comprises microballoons.
 14. The method of claim 8 wherein saidexplosively-launched vehicle is selected from the group consisting ofguided projectiles and missiles.
 15. The method of claim 8 wherein saidgranular material is tightly packed into said guidance electronics unitby vibrating said housing during filling.